Control circuit



Dec. 11, 1962 A. w. WILKERSON ETAL 3,063,394

CONTROL VCIRCUIT Filed Aug. 24. 1960 finnmlllill FIG 1 VAR/ABLE? 12 0. SOURCE mmvrons Alan W Wilkerson W/I/Iam J Bradbum United States Patent ()filice 3,068,394 Patented Dec. 11, 1962 3,068,394 CONTROL CIRCUIT Alan W. Wilkerson, Racine, Wis., and William 5. Bradhnrn, Jiu, Butler, Pa., assignors to The Louis Allis (10., Milwaukee, Wis., a corporation of Wisconsin Filed Aug. 24, 1960, Ser. No. 51,615 3 Ciaims. (431. 32322) This invention relates in general to a circuit arrangement for controlling power which is delivered to a load and, in particular, to a circuit arrangement whereby power 18 intermittently delivered to a load in response to a control signal.

For a given amount of power dissipation within an electron flow device such as a transistor or vacuum tube, a much greater amount of power can be controlled if the electron flow device is operated as a switch to effect the flow of current and voltage than if it is operated as a linear control amplifier with a continuous but variable output. This high power handling capacity of an electron ilow device is due to the fact that high voltage and high current through the electron flow device do not occur simultaneously, i.e., when the electron flow device is in the non-conducting or off state the voltage across the electron flow device is high but the current is negligible; conversely, when the electron flow device is in the conducting or on state there is a high current but almost no voltage due to the low resistance of the electron flow device.

Many schemes have been devised to utilize electron flow devices to control power by rapidly switching the electron flow device alternately between the on and off states, the average power to the load being controlled by the length of the on and olf periods. These circuits, however, have used triangular or sawtooth waveforms to accomplish the variation in switching times, a method which has several obvious disadvantages. It is necessary to provide a means of generating the special waveform. Additionally, the linearity or constant input-output relationship of the control is dependent on the linearity of the sawtooth or triangular waveform. Good waveform linearity requires a filtered power supply. Many circuits of this type require some form of initial adjustment for proper operation.

It is therefore an object of this invention to provide a new and improved circuit arrangement to control electric power.

it is a further object of this invention to provide a device for controlling power which is of simplified design and which requires no adjustment for optimum operation.

Another object of this invention is to provide a power control device which requires no special waveform or power supply for operation.

An additional object of this invention is to provide a power control device having a relationship between inut and output which is substantially linear over the entire range of operation.

Further objects and the manner in which they are achieved and numerous of the advantages of our invention will become apparent from the following detailed description and the annexed drawings wherein:

FIGURE 1 is a schematic circuit diagram of a power control system in accordance with one embodiment of the invention.

FIGURES 2, 3 and 4 are graphical illustrations of the operation of the system set forth in FIGURE 1.

Referring specifically to FIGURE 1, a power control system is shown therein having a power supply indicated generally by the numeral 16, a power regulation circuit 3t? and a switching transistor and associated elements indicated by numeral 20.

Power supply 10 is comprised of a source of alternating current 12 and a transformer 14 having rectified and nonrectified outputs. The fully rectified output is produced by a center-tapped secondary winding 16 and diodes 17. The non-rectified output is taken directly from secondary winding 19. The non-rectified output contains a reactive element which is designed to provide a substantially phase displacement between current and voltage and which in the drawings is illustrated as capacitor 18.

The power regulation circuit 30 has a variable source of unidirectional or direct current voltage, shown diagrammatically by box 32. This source must be capable of assuming either polarity. In practice this is generally a device producing a direct current signal corresponding to a function such as speed or position. Resistor 34 should be of a high impedance compared to the remainder of the circuit and thereby converts the variable direct current Voltage source 32 to essentially a current output device. The addition of resistor 34 somewhat isolates voltage source 32 from the remainder of the circuit. The current which will flow from source 32 will not be affected by normal variations in the impedance of the remainder of the circuit. However, to insure that the variations in impedance are not too large, diode 23 is inserted in the circuit as will become more understandable hereinafter.

Switching transistor 21 may be either the PNP or NPN type, the PNP type being shown in FIGURE 1. The emitter and collector terminals of this transistor are connected across the rectified output of power supply 10 in a manner such that current will flow when the transistor is in a conducting state. In series with either the emitter or collector terminal of transistor 21 is the load 40 shown diagrammatically and which may be an eddy current clutch or motor winding.

The power regulation circuit 30 is connected to the base and emitter terminals of transistor 21. In parallel with the power regulation circuit is placed the unrectitied portion of the output of power supply 10. Also in parallel is diode 23 which provides a by-pass when transistor 21 is in the non-conducting state.

In operation, the control of power to the load is produced in the following manner. Activation of the power supply allows unrectified alternating current to flow from transformer secondary 19 through capacitor 18 to the base and emitter terminals of transistor 21. Current at the emitter and base terminals is 90 out of phase with respect to the voltage from secondary winding 19. The subsequent path of the current depends upon the polarity of the current. When the polarity of the alternating current is positive, transistor 21 cannot conduct; however, diode 23 is then in a conducting state and the current circulates through diode 23. When, however, the polarity of the alternating current is negative, diode 23 cannot conduct and the current is allowed to circulate through the transistor 21, entering the emitter and leaving at the base. The negative polarity of the base of transistor 21 permits the rectified output from transformer secondary 16 to circulate through the emitter and collector terminals of transistor 21 and through the load. Since the current in the unrectified output is 90 out of phase with the voltage in the rectified portion, due to capacitor 13, the load will be supplied with power during the last half of one rectified half wave and the first half of the succeeding one. This operation is described graphically in FIGURE 2, wherein 50 is the rectified portion of the output of transformer secondary 16; 52 is the current in the unrectified output of transformer secondary 19; and 54 represents the period during which transistor 21 is in the conducting state.

The variable, bipolar direct current source 32 affects the above operation by controlling the period of conduction, thereby attesting the length of time during which the base terminal of transistor 21 is negative with respect to the emitter. If the direct current source 32 is placed at a negative polarity and added to the alternating current from transformer secondary 19, the period during which the combined current is of negative polarity will be increased, thereby allowing the transistor 21 to conduct for a longer time interval, increasing the portion of each current half Wave from transformer secondary 7.6 which is circulated to the load. Increasing the negative polarity to a value greater than the positive peak of the alternating current allows the transistor to conduct continuously, supplying maximum power to the load. FIG- URE 3 illustrates the operation of the control when the polarity of direct current source 32 is negative. The combined current signal from the unrectified portion of transformer secondary 19 and from direct current source 32 is shown by 56.

From the foregoing it is obvious that a positive current from direct current source 32 will decrease the conducting period of transistor 21 and the power to the load, as shown in FIGURE 4.

The theoretically linear operation of the control can be shown by the following mathematical analysis and by reference to FIGURES 2, 3 and 4. The period of conduction or conduction time is determined by the polarity of the sum (I) of the current from the direct current source (I and the current from the unrectified output of transformer secondary 19 (i or ti' dc The value of I at any instant of time is 1:1 cos H-l-I where is the angular displacement along the time axis and I is the maximum value of I The transistor switches on or oil when the sum I equals zero. Thus,

1 mm sin O 1r 0 resulting in E *"-[-cos 010 Since da -cos 0= the area 513 or the non-conducting portion of the cycle equals 77' L In all However, E and 1 are constants in the system and therefore it can be seen that the average current or the amount of current which is delivered to the load is a linear function and directly proportional to The phase displacement between the current at the emitter and base terminals and the voltage from second- ;ary winding 19 need not be 90. Any lesser amount of displacement may be used, the only change in the operation of the system being a decrease in its linearity.

Numerous modifications may be made to the above control system without departing from the spirit oi the invention. For example, gas filled tubes or other unidirectional devices capable of being switched on and 0t? on the same conditions may be used in place of the transistors described above. While the embodiment above is at present considered to be preferred, it is understood that various modifications may be made therein, and all such modifications and improvements fall within the true spirit and scope of the invention.

What is desired to be claimed and secured by Letters Patent of the United States is:

1. A circuit arrangement for controlling the power which is delivered to a load in response to a control sie comprising, a power source providing a unipolar periodically varying current and voltage wave pattern, a load device, an electron fiow control device having common terminal and an output terminal and a control terminal, said load device and said power source being connected in series across said common terminal and said output terminal, a first control signal source connected to the control terminal of said control device providing a substantially constant but variable signal, a second control signal source connected in parallel with said first control signal source and connected to the control terminal of said control device providing a bipolar periodically varying current wave pattern, the period of which is a multiple of the period of said wave pattern of said power source and out of phase therewith, said control device having a conduction threshold signal level predetermined at said control electrode, whereby said control device is rendered selectively conductive and non-conductive in accordance with the instantaneous signal level provided by the composite of said control signals from said first and second control signal sources.

2. A circuit arrangement for controlling the power which is delivered to a load in response to a control signal comprising, an alternating current source, rectifier means connected to said source for providing a unipolar periodically varying current and voltage wave pattern, a load device, an electron flow control device having a cemr on terminal and an output terminal and a control termi said load device and said rectifier means being conne ed in series across the common terminal and the output terminal of said control device, means including a rcactance element connected in a series loop between said alternating current source and the common and control terminals of said electron fiow device thereby to provide a bipolar periodically varying wave pattern, the period of which is a multiple of the period of said unipolar wave pattern and. substantially 90 out of phase therewith, and a direct current source providing a bipolar amplitude variable signal connected between the common terminal and the control terminal of said electron control device, said electron fiow device having a conduction threshold signal level across said common terminal and said control terminal, whereby said electron flow device is rendered selectively conductive and non-conductive during periods of said unipolar periodically varying signal in accordance with the instantaneous level provided by the composite of said bipolar variable signal and said bipolar periodically varying signal so as to provide power to said load device directly in accordance with the signal level of said bipolar variable signal.

3. A circuit arrangement for controlling the power which is delivered to a load in response to a control signs comprising, an alternating current source, a transformer having a primary winding and a first and second secondary winding, said first secondary winding being centertapped, said alternating current source connected to said primary winding. said first secondary winding having rectifiers connected thereto, the output from which provides a unipolar periodically varying current and voltage wave pattern source, a load device, a transistor control device having emitter, collector and base terminals, said emitter and collector terminals connecte a series loop with said load device and the output of said rectiiicrs and in such a manner as to tend to place said transi i in the conducting state, said second secondary of transformer connected in a series loop with a reactance eleout and said emitter and base terminals thereby to provide a bipolar periodically varying Wave pattern, the period of which is a multiple of the period of said unipolar Wave pattern and substantially 99 out of therewith, said emitter and base terminals also connected in a series loop With a variable bipolar direct curr nt voltage source and a resistor, said resistor adapted to be of such a value as to convert said variable bipolar direct current voltage source to a variable bipolar current source,

said transisto .ving a conduction tliresl". ld s' across emitter and base terminals whereby sai sister is rendered selectively conductive and non-conductive during periods of said unipolar periodically varying nal in accordance with the instantaneous level prod by the co aosite of said variable bipolar current source and said bipolar periodically varying Wave pattern source so as to provide power to said load device directly in accordance with the signal level of said variable bipolar current source.

References in the file of this patent FOREEGN PATENTS 564,582 Canada Oct. 14, 1959 

